DE3782460T2 - THIN FILM WITH LARGE KERR ROTATION ANGLE AND METHOD FOR THE PRODUCTION THEREOF. - Google Patents

Description

The invention relates to a thin film of a magneto-optical material, particularly to a thin film having a large Kerr rotation angle, and to a thin film capable of exhibiting transparency and transverse magnetic anisotropy, and a manufacturing process thereof.

As an optical technology that makes use of the magneto-optical Kerr effect, magneto-optical recording has now emerged. The present invention is satisfactorily applicable to optical recording media that are indispensable for magneto-optical recording.

As magneto-optical materials with a large Kerr rotation angle there are halogen compound systems, typically CrX₃ (X: Cl, Br or I). This material shows a rotation angle of RK = 3.5º near 425.5 nm at a low temperature of 1.5 K.

Among the oxygen systems, there are not many materials that exhibit a large Kerr rotation angle. However, CoFe₂O₄ and Eu₃Fe₅O₁₂ can be cited as examples. CoFe₂O₄ has been reported to exhibit RF = 3.3·10⁴ deg/cm at 780 nm and exhibit RK = 0.6° when enhanced by a reflecting plate. In the case of Eu₃Fe₅O₁₂, a value of RK = 0.17° (at 297 nm) has been reported.

There are a variety of magneto-optical materials among the metal systems. As polycrystalline materials, thin MnBi alloy films and thin PtMnSb-Heusler alloy films can be mentioned. These thin PtMnSb films show an RK = 1.82º (at 5 kOe) at 725-716.7 nm and room temperature. However, no perpendicular magnetic films have been prepared so far.

If we now turn to amorphous materials, transverse magnetic films can be obtained from rare earth systems. These show an RK = 0.3-0.40.

Metallic materials are accompanied by the inherent problem that they lose optical transparency at a film thickness of about 100 nm (1,000 Å), especially when a semimetal such as Mn is included.

The following properties can be specified as typical properties required for magneto-optical recording media:

(1) Transverse magnetic film:

It is necessary that these are perpendicular magnetic films in order to achieve high recording density. Relation K> 2πMs² (K: perpendicular magnetic anisotropy constant, Ms: saturation magnetization) should be satisfied.

(2) Writing performance:

Since methods of thermally writing information in a perpendicular magnetic film are used, the thermomagnetic recording characteristics at the Curie point, the thermomagnetic recording at the compensation point, etc. can be mentioned. From the parallel consideration of the thermal stability of the recorded information and the desire for a small recording energy, a temperature increase of 100 to 200ºC seems to be suitable.

(3) SN ratio (signal-to-noise ratio):

The following reasons can be considered as sources of noise in magneto-optical storage devices:

i) Changes in a light source.

ii) Noise generated by a medium.

(iii) noise attributable to deficiencies in a sensing device and/or a polarising device.

iv) Noise of an amplifier in an amplifier circuit for an electrical signal.

S/NαR·RK (R: reflectance of the film, RK: Kerr rotation angle). However, to increase the S/N ratio, it is necessary to reduce the noise, increase the reflectance of the material and increase the effective Kerr rotation angle.

(4) Stability and possibility of easy manufacturing:

i) The medium should be mechanically, thermally and chemically stable. It should allow multiple write operations and long-term storage.

ii) The disks should be easy to manufacture. The cost per bit should be reasonable.

Magneto-optical materials have both advantages and disadvantages.

When the magneto-optical Kerr effect is used, the primary purpose is to produce a magneto-optical recording medium. An extremely large number of materials have been developed to date that make use of the magneto-optical Kerr effect.

Initially, MnBi attracted attention. In view of the increased disadvantages of MnBi that it has a high Curie temperature and is subject to phase transitions, MnSb, MnAlGe and Mn1-xTixBi were subsequently developed. However, it was CuMnBi that had the best data among the polycrystalline media as a magneto-optical disk. Since CuMnBi is polycrystalline, the most serious problem of this material is considered to be that it generates large material noise. On the other hand, PtMnSb, which shows the largest Kerr rotation angle at room temperature, requires heating at a high temperature and for a long time to form a superlattice like a Heusler alloy. In addition, it cannot be converted into a perpendicular magnetic film as shown above. It is therefore not a material that can be used at present. CoFe2O4 is also of interest after amplification because of its large Faraday rotation angle. However, it also requires a refractory substrate for vacuum deposition. Some materials with very large performance indices R·RK have been discovered among the uranium compounds. However, their Curie temperatures are below room temperature, making them impractical.

It could be considered to use either a single crystal or an amorphous material to avoid intercrystalline noise, which is an inherent disadvantage of polycrystalline materials. Among the single crystal materials, GdIG (or a perpendicular magnetic film of BiYIG) has a compensation temperature, which is close to room temperature, and its performance index 2F/α (F: Faraday rotation coefficient, α: absorption coefficient) is sufficiently large as a Faraday device. However, α is small. Therefore, a thick film is required. The above material is therefore accompanied by such problems that difficulties arise in reducing bit dimensions and also in producing a large disk-like recording medium and the production cost is high. Researches are now underway using metals and oxides with a view to producing a desired medium on a substrate by forming a multilayer film in which atoms are stacked in groups of several atoms per layer. However, none of these researches has resulted in a practically useful material.

From the point of view of practical utility, the development of amorphous alloy materials of rare earth element Co and Fe (transition metal) is now the subject of a large series of works and practical data are reported.

Next, a description of amorphous rare earth transition metal films is made.

(1) Saturation magnetization, Ms:

The spins of rare earth elements and a transition metal of the iron group are arranged in antiparallel alignment. The magnetic moment of the rare earth element and the transition metal of the iron family is therefore the sum of both sublattices in the case of a rare earth element and the difference between both sublattices in the case of a heavy rare earth element. In the case of a heavy rare earth element, Ms, Hc and Tc can therefore be determined by selecting the composition. It is It is thus possible to satisfy the condition for a transverse magnetic film, namely K>2πMs², so that the formation of a transverse magnetic film is facilitated.

(2) Transverse magnetic anisotropy, K:

A rare earth transition metal film has a large transverse magnetic anisotropic energy, which can be attributed, for example, to:

i) an oriented arrangement of rare earth atom pairs and a magnetic anisotropy; and

ii) a form of anisotropy due to a film structure such as a prismatic structure and internal strain and magnetostriction of the film.

Since the transverse magnetic anisotropy varies slightly with the Ar partial pressure and composition, the large transverse magnetic anisotropy energy has not been fully elucidated with respect to its origins.

(3) Coercivity, Hc:

The mechanism of the appearance of the coercivity has not been elucidated. If a single cylindrical magnetic domain with opposite magnetization occurs in a perpendicular magnetic film, the minimum diameter of the domain, dmin, that can remain stable is approximated by:

dmin = σw/Ms·Hc

where σw is the energy density of the domain wall and Hc is the coercivity of the film. A high-density recording medium requires a high degree of transverse magnetic anisotropy and a coercivity of several kOe. In this respect, rare earth elements can satisfactorily meet these conditions.

(4) Kerr rotation angle, RK:

Since the magnetic field dependence of the Kerr rotation angle of rare earth element transition metal films is shown by similar plots as their M-H curves in many cases, the Kerr rotation angle is assumed to be proportional to M. However, it is not very large, namely 0.3 to 0.4º.

The main disadvantage of amorphous rare earth transition metal films is that they are susceptible to oxidation and consequently are subject to deterioration if left without protective films. There is the other problem that optimal conditions for their preparation are difficult.

The current magneto-optical recording media are primarily made of rare earth element-transition metal systems as described above. However, the Kerr rotation angles (RK) of these media are on the order of 0.3º to 0.4º. Compared with other optical recording devices, e.g., a system in which the reflection intensity is read by using the roughness of a medium, these are accompanied by a disadvantage that their S/N ratios are small, namely, below 60 dB. For this reason, they are prone to errors and are usable only in certain limited areas. Their advantage of allowing overwriting cannot be fully utilized.

However, there is a great need for the development of a recording medium having a large Kerr rotation angle and a film capable of increasing the Kerr rotation angle.

It is an object of the present invention to provide a halogen-containing ferromagnetic transparent film which, despite bonding with the halogen atoms, does not cause an excessively large peak shift compared with a 3d transition metal (Fe, Co or Ni) in an X-ray spectrum, in other words, is metallic, maintains ferromagnetism, gives a large amount of reflected light, and has transparency, a large Faraday coefficient and a large Kerr rotation angle thanks to the insertion of halogen atoms, in particular a halogen-containing transparent film having perpendicular magnetic anisotropy, and a manufacturing process thereof.

According to one aspect of this invention, there is thus provided a thin film (hereinafter referred to as "halogen-containing thin transparent film") having a large Kerr rotation angle comprising a compound having a composition represented by the following formula (I):

JxLyQ(100-x-y) (I)

where

J: represents an element selected from the elements F, Cl, Br and I or a combination thereof ;

L: an element of one of the element symbols B, C, Al, Si, P, As, Sb, Bi, Se, Te, Ti, V, Cr, Mn, Ga, Ge, Zr, Nb and Mo or a combination thereof;

Q: is one of Fe, Ni or Co or a combination thereof;

x: is a value between 3-80; and

y: is a value that satisfies the following equation (II):

3 ≤ x + y ≤ 80 (II)

The thin film preferably exhibits both transparency and transverse magnetic anisotropy. Namely, it is a preferably transverse magnetic thin transparent film (this preferably thin film is hereinafter referred to as a "transverse magnetic thin transparent film").

According to a further aspect of this invention, there is also provided a method for producing a halogen-containing thin film having a large Kerr rotation angle and composed of a combination of the compositions described above, which comprises reacting a halogen or a halogen-containing gas resulting as a result of the segregation of a halogen composition with a metal plasma or halogen-containing metal plasma and allowing the resulting mixture to deposit as a thin film on a substrate.

The present invention has provided several advantages, including the following representative advantages:

(1) The halogen-containing thin transparent film of this invention has a large Kerr rotation angle (RK) of 0.5° at an F content of 50 at% (atomic %) in the wavelength range of the HeNe laser. At 700 to 800 nm, RK increases to 0.7°. It can therefore be suitably used for magneto-optical recording media that make use of the magneto-optical Kerr effect.

(2) The halogen-containing thin transparent film of this invention contains chemical bonds which do not cause peak shifts with respect to the Lα and Lβ lines in its X-ray emission spectrum even if it has a high halogen content. It therefore exhibits ferromagnetism and optical transparency.

(3) The hysteresis of the RK-H curve of the transverse magnetic thin transparent film according to this invention has a typical curve for transverse magnetic films. Although the transverse magnetic thin transparent film itself can serve as a magneto-optical recording material, it can be combined with another transverse magnetic film such as a TbFeCo film so that a still larger Kerr rotation angle can be obtained due to the provision of the amplification and the combined Faraday rotation. The thus combined material is very useful as a magneto-optical disk recording medium.

(4) The halogen-containing transparent thin film can be obtained by the production process of this invention in any of amorphous, crystalline or metastable forms. It is also possible to control the degree of desired chemical bonds as desired. It is also feasible to change the proportions of J and L in the compositions of the above formula (I) as desired so that the halogen-containing transparent thin film having a desired large rotation angle is obtained.

(5) According to the manufacturing method of this invention, a highly reactive halogen gas is not directly introduced into a manufacturing apparatus. The materials of the manufacturing apparatus are therefore not corroded. This prevents impurities from mixing with the thin film to be deposited.

The above and other objects, features and advantages of the present invention will become apparent from the following description and appended claims taken in conjunction with the accompanying drawings in which:

Fig. 1 shows the profile of soft X-ray spectra of films of Fe and Fe-Fn compounds (n: 2, 3) or those of films of the invention with a large Kerr rotation angle;

Fig. 2 is a graph showing the peak position of Lα and Lβ of iron, the peak height ratios of Lα/Lβ and the half widths of Lα in the X-ray spectra of the films of the present invention having large Kerr rotation angles, in comparison with the Fe, FeF2 compounds and FeF3 compounds;

Fig. 3 graphically shows the Fe dependence of the saturation magnetization Ms of a Fe-B-F film and that of the average magnetic moment uFe (uB per iron atom);

Fig. 4 graphically shows the wavelength dependence of the Kerr rotation angle RK of a Fe-B-F film and the magnetic field dependence of the Kerr rotation angle RK of Fe44.0B3.6F52.4 in the He-Ne laser;

Fig. 5 shows the M-H hysteresis curve of a transparent and transversely magnetic Fe40F60 film;

Fig. 6 is a simplified schematic view of an opposing target radio frequency direct current (DC, Rf) sputtering apparatus used in the examples of this invention;

Fig. 7 is a graph showing the Fe dependence of the Kerr rotation angle of a sputtered Fe-B film and a Fe-B-F film, both prepared in the He-Ne laser using Fe90B10;

Fig. 8 shows an RK-H hysteresis curve in a transparent and perpendicular magnetic film of Fe40F60 in the He-Ne laser;

Fig. 9 is a plan view of a plate made of glass or a resin;

Fig. 10 shows an RK-H hysteresis curve of a perpendicular magnetic TbFeCo film;

Fig. 11 shows an RK-H hysteresis curve of a perpendicular magnetic film of Fe40F60 + TbFeCo;

Fig. 12 schematically illustrates a system making use of a medium according to this invention, which enables recording by a perpendicular magnetic recording head and scanning by an optical head;

Fig. 13 an RK-H hysteresis curve of a Fe-F film versus the optical transmission of a He-Ne Laser and the magnetic field dependence of the magnetization; and

Fig. 14 shows the magnetic characteristics of a Ni-F film and its RK-H hysteresis curve.

The present invention will now be described in detail below.

The above halogen-containing thin transparent film and the perpendicular magnetic thin transparent film can have various crystalline structures. Namely, they can take an amorphous, crystalline or metastable state. Since their interatomic bonds have essentially no influence on the 3d orbital, they do not exert much influence on the magnetic characteristics of the transparent film. The above thin films therefore exhibit metallic and ferromagnetic properties and these films exhibit transparency by the halogen element or elements which exhibit light transparency. Due to their metallic nature, they can give a large reflectivity. By adding rotations of light-deflecting angles both on the surface of the films and within the films, they exhibit large Kerr rotation angles by reflection.

The above films having the large Kerr rotation angles are applicable as optical modulators utilizing the magneto-optical Kerr effect in magneto-optical and optical integrated circuits such as optical switches, optical isolators and circulators. In magneto-optical disk storage devices utilizing the magneto-optical Kerr effect, the Kerr rotation angles can be further increased by using a multilayer structure utilizing both the magneto-optical Kerr effect and the Faraday effect. in combination. In view of this wide-ranging applicability, they are indispensable for current and future optical technologies.

As characteristic properties of the halogen-containing thin transparent film according to this invention, the following properties can be shown.

a) Its chemical bonds do not cause significant chemical shifts of the Lα spectral line in a soft X-ray emission spectrum, even if the element F is present at 50 at.% or similar.

b) Therefore, it can generate a large magnetization. As a material capable of exhibiting optical transparency, its magnetization is at least 60 emu/g with an F content of about 50 at.%. The average magnetic moment uB per Fe atom is about 1 uB.

c) The Kerr rotation angle increases proportionally to the proportion of F. With an F proportion of 50 at.%, a rotation angle of 0.5º is observed in the wavelength range of a He-Ne laser. A rotation angle of 0.7º is observed at 700 to 800 nm.

The transverse magnetic thin transparent film according to this invention has the following property d) in addition to the properties a) to c) described above.

d) A film exhibiting transverse magnetic anisotropy can be formed by specifying its preparation conditions, i.e., the final pre-vacuum pressure, the argon partial pressure, the sputtering temperature and the sputtering power.

The above properties a)-d) are described in further detail below.

a) Halogen atoms react with some metals and also react with many non-metals. Of such halogen atoms, F is the most reactive. The reactivity decreases as the number of atoms increases. This high reactivity of the element F is due to the low energy of an F-F bond, its extremely strong oxidation energy and its high electronegativity.

Because of this violent reactivity, halogen gases are not present in metals in various proportions. They have been used primarily as reactive gases in the dry etching technique or as carrier gas in the chemical vacuum vapor deposition process.

Upon chemical bonding with a metal, a halogen element is transformed into a crystal with optical transparency. However, it is the general characteristic of halogen compounds such as FeF2 and FeF3 shown in Fig. 1 that a considerable Lα line shift is observed along with an increase in line width, causing a significant influence on the 3d level of the electronic state of Fe and exhibiting antiferromagnetism or parasitic ferromagnetism.

It is a characteristic feature of the manufacturing process of this invention that the Lα line shift is small. The profiles of Lα and Lβ peaks in a soft X-ray emission spectrum of Fe in the halogen-containing thin transparent film of this invention are shown for various halogen contents in Fig. 1. Fig. 2 shows the shift of the Lα and Lβ peaks, the ratios of the Lα peak height to corresponding Lβ peak heights, namely Lα/Lβ (height ratio), and the F content dependence of the half-width of the Lα peaks in comparison with the corresponding data of Fe, FeF₂ and FeF₃.

As is clear from Fig. 1 and Fig. 2, the halogen-containing thin transparent film according to this invention, e.g., the Fe-B-F film, shows the same Lα and Lβ peak positions and peak half-widths as Fe, and the height ratio of Lβ/Lα increases as the content of the element F increases. It is therefore clear that no Lα peak shift occurs, unlike FeF₂ or FeF₃. This means that the chemical bond Fe-F is formed between the respective outermost orbitals, and the inner orbital which significantly influences the magneto-optical effect, namely, the 3d orbital, is not influenced. The halogen-containing thin transparent film according to this invention is therefore ferromagnetic and exhibits a large magneto-optical effect due to, for example, the effect of the magnetic moment of the electron on the orbital of the 3d level.

b) Fig. 3 shows the Fe dependence of the saturation magnetization Ms of the Fe-B-F film and that of the average magnetic moment uFe(uB per iron atom). Due to the existence of such an electronic state as described in a) above, good optical transparency and high magnetic characteristics are exhibited even at an F content of about 50 at.%.

The element F is an amorphous element, in which no major changes occur in terms of the Curie temperature and the crystallization temperature, even when the F content increases.

However, the saturation magnetization Ms becomes smaller as the F content decreases. When the fluorine compound starts to grow in the amorphous phase, the degree of reduction of Ms is reduced. uFe (at 77 K) decreases in the amorphous phase as the F content increases. However, uFe reaches about 1 uB when a fluoride phase appears.

This is a typical reflection of the Fe-F bonds.

c) Due to such characteristic electronic state of metal gas elements as described above, the amount of reflected light is large, with the Kerr rotation angle increasing as the F content increases. At F contents of 40-50 at.%, large Kerr rotation angles are shown, namely RK = 0.5º at the wavelength range of a He-Ne laser and RK = 0.7º at 700-800 nm.

Fig. 4 shows an example of the wavelength dependence of the Kerr rotation angle RK of Fe-BF films. The films plotted in Fig. 4 are in-plane magnetizable films. In terms of their dependence on the magnetic field, their rotation angles at 633 nm increase as the magnetic field becomes stronger. The larger the content of F, the larger RK·RK tends to continue to increase towards longer wavelengths. The special Fe-F bond and the optical transparency of the element F seem to be combined in such a way that the resulting rotations on the surface of the film and within the film probably contribute to the formation of a large Kerr rotation angle. In the case of oxides, Kerr rotation angles by reflection without reflection plates are usually extremely small. The Film according to this invention shows a large Kerr rotation angle without a reflection plate.

d) Turning next to the transverse magnetic thin transparent film, it is an in-plane magnetizable film. However, it can be obtained as a transparent film providing transverse magnetic anisotropy if the conditions for forming the film are appropriately selected. In Fig. 5, M-H hysteresis curves of Fe40F60 films are shown as examples. From the in-plane and transverse directions, clear anisotropy is shown in the transverse direction. The vertical magnetic anisotropy energy has a positive value.

The method for producing the halogen-containing thin transparent film according to this invention makes use of a reactive film forming method. This method is carried out in a state in which at least one of the components of a compound to be formed in the form of a thin film is maintained in a gas phase.

A reactive radio frequency direct current (Rf, DC) sputtering device can be used as a manufacturing device, for example. This reactive sputtering includes both physical sputtering and chemical sputtering. A thin film is formed on a substrate at a low temperature and in a state where the impact energy on the substrate is low. Due to the reactive sputtering, it is possible to vary the gas partial pressure and the power output to the target, so that optically transparent films in various structures, namely the amorphous, the crystalline and the metastable form, can be obtained. It is also possible to determine the degree of chemical bonds (ionization degree) at different levels.

A halogen compound is dissolved in the manufacturing process of this invention, whereby a halogen gas and its compound gas are produced as reactive gases. These halogen gases then react with a metal plasma, which may contain the same type of halogen gases, allowing the resulting compound to deposit as a thin film on the substrate. This process has the advantages of avoiding the risk of introducing a highly reactive halogen gas through a piping system and also preventing the incorporation of contaminants.

The present invention is described in more detail below by the following examples.

example 1

A DC,Rf sputtering apparatus with opposing targets as shown in Fig. 6 was used. Fe90B10 (at.%) was applied to opposing DC targets 1, which were cooled with water.

An Rf target 2 is made by press-making a halogen compound, FeF₃₁. After the inside of a vacuum vessel is evacuated to 3.99 to 6.65·10⁻⁷ mbar (3 to 5·10⁻⁷ Torr), Ar gas is introduced to raise the internal pressure of the vacuum vessel to 1.33·10⁻² mbar (1·10⁻² Torr). Also shown are a DC power supply 4, a substrate 5, an argon gas supply port 6, a pump port 7, a water-cooled substrate holder 8, an Rf power supply 9, and a matching circuit 10.

By setting the Rf output for the production of the halogen gas to, for example, 300 W and changing the DC output of the opposing DC-Fe90B10 targets 1, it was possible to easily vary the content of B and F in an optically transparent film to be formed on the substrate 5. Their crystalline structures were amorphous at F contents of 25 at.% and below, while at F contents above 25 at.% peaks corresponding to the X-ray diffraction of fluoride crystals appeared.

Fig. 7 shows the Fe dependence of the Kerr rotation angle of sputtered Fe-B films and that of the Kerr rotation angle of Fe-B-F films made from Fe90B10, both in the He-Ne laser. At about 50 at.% Fe, an RK of 0.5° was shown.

The value of RK can be improved by including Co and/or one or more of the elements recited in the claims in the Fe-B-F film.

Example 2

When such a sputtering device as shown in Fig. 6 was used, the water-cooled substrate holder 8 was rotated by 180° so that the substrate 5 was aligned with the side of the Rf target 2.

The Rf target 2 was prepared by press-making the halogen compound, for example, FeF₃. After the inside of the vacuum vessel was evacuated to 3.99 to 6.65·10⁻⁷ mbar (3 to 5·10⁻⁷ Torr), Ar gas was introduced to raise the internal pressure of the vacuum vessel to 6.65·10⁻³ mbar (5·10⁻³ Torr).

By setting the Rf output power of the FeF₃ target produced by pressing to, for example, 250 W was allowed to deposit on the substrate 5. The magnetic characteristics of a sputtered film thus obtained were measured by VSM (Vibration Magnetometer). As a result, a film having transverse magnetic anisotropy, namely, a large magnetic anisotropy in a direction perpendicular to the plane of the film, was obtained, for example, as shown in Fig. 5. In addition, the magnetic field dependence of the Kerr rotation angle via reflection by the Fe-F film was determined. An RK-H hysteresis curve as shown in Fig. 8 was obtained. The value of RK was measured to be 0.320 with a He-Ne laser. This value further improved on the longer wavelength side. It was also improved when a reflective plate was applied.

The Faraday rotation angle of a Fe-F film via the transmission of a He-Ne laser and the magnetic field dependence of the magnetization were then determined. An RK-H hysteresis curve was obtained as shown in Fig. 13. The Faraday coefficient was found to be 2.2 104 deg/cm. The shape of the RF-H hysteresis curve was similar to that of the M-H curve of M, which is shown above the RF-H hysteresis in the same figure. An RK-H hysteresis curve was also obtained using a reflective plate. The value of RK in a magnetic field of 557.04 kA/m (7 kOe) was 2.20°.

The transverse magnetic anisotropy energy and RK can be improved by incorporating one or more elements such as Co and others recited in the claims in the Fe-F film.

Example 3

In the same manner as in Example 2, NiF2 was provided by press-making as an exemplary halogen compound for the Rf target 2. After the inside of the vacuum vessel 3 was evacuated to 6.65·10⁻⁷ mbar (5·10⁻⁷ Torr), Ar gas was introduced to set the inside pressure of the vessel to 6.65·10⁻³ mbar (5·10⁻³ Torr).

While the Rf output of the NiF2 powder target prepared by pressing was kept at, for example, 250 W, a sputtered film was allowed to deposit on the substrate 5. The magnetic characteristics and Faraday rotation angle of the resulting sputtered film were measured. A perpendicular magnetic film was obtained which had a positive perpendicular magnetic anisotropy energy in a direction perpendicular to the surface of the film, as shown in Fig. 14. In addition, the magnetic field dependence of the Faraday rotation angle of the Ni-F film was determined with a He-Ne laser light source. The magnetic field dependence of RF is shown in the lower part of Fig. 14. It has a similar shape to the M-H hysteresis curve of M shown in the upper part of Fig. 14.

A reflective plate was placed on the Ni-F film and the Kerr rotation angle was measured. It was found to be 1.210 using a He-Ne laser. The Kerr rotation angle was found to be 0.7º at H = 0.

The transverse magnetic anisotropy energy and RK can be improved by incorporating one or more of Fe, Co or other elements recited in the claims in the Ni-F film.

As examples, compositions of thin film samples containing halogen elements falling within the compositions recited in claim 1, exhibiting optical transparency and a perpendicular magnetic anisotropy, and having a large Kerr rotation angle are shown in the following table, together with their Kerr rotation angles. Table Example Composition, at.% Kerr rotation angle, degrees

Example 13

Using the sputtering apparatus shown in Fig. 6, a glass or resin disk of 200 mm x 35 mm x 1.2 mm thick shown in Fig. 9 was set on the water-cooled substrate holder 8. The disk was rotated at 20 to 200 rpm from outside the vacuum vessel 3. Fine particulate metals such as Co, Bi and Te containing FeF₃ powder, for example, were placed on the Rf electrode so as to cause an optically transparent and transversely magnetic film at 50 nm (500 Å) on the glass plate. TbFeCo was then placed on the Rf electrode so that it was deposited on the film at 150 nm (1,500 Å). A protective layer of SiO was then deposited on the TbFeCo film at 10 nm (100 Å).

A magneto-optical disk manufactured in the above manner has the following characteristics.

An RK-H hysteresis curve of a perpendicular magnetic film made of TbFeCo alone is shown in Fig. 10. The hysteresis of RK has a similar shape to the shape of the Ms-H hysteresis curve measured by VSM, indicating that the TbFeCo film was a perpendicular magnetic film. Its Kerr rotation angle RK was 0.2° in the He-Ne laser.

An optically transparent and perpendicular magnetic film of 50 nm (500 Å) according to this invention was then deposited on the disk in advance, followed by the deposition of a TbFeCo film having a thickness of 150 nm (1,500 Å). The RK-H hysteresis curve of this thus prepared film substantially reproduces the hysteresis of the RK-H curve of TbFeCo as shown in Fig. 11. Its RK was found to be 0.7° within the wavelength range of the He-Ne laser. This value increases toward the longer wavelength side. Then, the S/N ratio of the thus prepared magneto-optical disks was determined. An LED (wavelength: 800 nm) was used as a light source. The S/N ratio was found to be at least 60 dB.

As demonstrated above, the optically transparent and transversely magnetic film according to this invention is effective in amplifying of the Kerr rotation angle effectively, so that the value of RK increases.

Example 14

The use of an optically transparent and perpendicular magnetic film according to this invention as an optical recording medium will next be described by way of example.

Fig. 12 schematically shows a system using the medium of this invention, which enables writing with a transverse magnetic head and optical reading (transverse magnetic recording and magneto-optical reading system). Reference numeral 11 designates a glass disk or a resin disk. Reference numeral 12 designates the optically transparent and transverse magnetic film of the invention. Reference numeral 13 designates a transverse magnetic film of a rare earth element Fe-Co system. This film is not required in every case. Also shown is a plate 14, which serves not only as a reflective plate but also as a plate for lubricating a slider of a transverse magnetic recording head 15.

The above system is described in detail below. This system has been developed to avoid the disadvantages of the current magneto-optical recording systems. The optical disks 11-14 are rotated at a high speed of 1,000 to 1,800 revolutions per minute (rpm). The transverse magnetic head 15 is spaced at a distance of about 5 nm (50 Å) from the protective plate 14. High frequency recording is performed in the films 12, 13 as recording layers by the head 15. Although the reference numeral 13 indicates the transverse magnetic film of the rare earth element Fe-Co system, the film 12 has the same properties as the film 13. Therefore, information can be first recorded in the optically transparent and perpendicular magnetic film 12. Written magnetic domains are more stable when recorded in the multilayer film. The thus written magnetic domains are then read out by a laser beam as shown in Fig. 12. The laser system is used exclusively for reading. Consequently, the output power of a semiconductor laser can be low and the stability of the laser beam source can be high. In addition, the temperature of the recording medium does not increase significantly because it is no longer necessary to perform recording at the compensation or Curie temperature. The stability of the recording medium has thus been significantly improved compared with the current magneto-optical recording systems. Since it is a recording method not accompanied by thermal diffusion, the writing, reading and overwriting speeds can be increased over those of current hard disks.

It is also possible to overcome the disadvantages of the perpendicular magnetic recording method. It is the disadvantage of the vertical magnetic recording method that a high S/N ratio cannot be fully ensured during reading if the written bit areas are made smaller. However, the system utilizing the present invention enables the use of small bit areas because the reading is carried out magneto-optically. The recording density can therefore be kept substantially at the same level as that of currently used magneto-optical systems.

As described above, the use of the optically transparent film having transverse magnetic anisotropy according to this invention makes it possible to highly stable recording system with the features of high-speed and high-density writing with high-speed reading and high-speed erasing.

Claims (3)

1. A thin film having a large Kerr rotation angle, containing a compound having a composition represented by the following formula (I): JxLyQ(100-x-y) (I) where J: represents an element selected from the elements F, Cl, Br and I or a combination thereof ; L: represents an element of any of the element symbols B, C, Al, Si, P, As, Sb, Bi, Se, Te, Ti, V, Cr, Mn, Ga, Ge, Zr, Nb and Mo or a combination thereof; Q: is one of Fe, Ni or Co or a combination thereof; x: is a value between 3-80; and y: is a value that satisfies the following equation (II): 3≤x + y≤80 (II) 2. The thin film of claim 1, wherein the film has optical transparency and perpendicular magnetic anisotropy. 3. A process for producing a halogen-containing thin film having a large Kerr rotation angle and composed of a compound of a composition represented by the following formula (I): JxLyQ(100-x-y) ) where J: represents an element selected from the elements F, Cl, Br and I or a combination thereof ; L: represents an element of any of the element symbols B, C, Al, Si, P, As, Sb, Bi, Se, Te, Ti, V, Cr, Mn, Ga, Ge, Zr, Nb and Mo or a combination thereof; Q: is one of Fe, Ni or Co or a combination thereof; x: is a value between 3-80; and y: is a value that satisfies the following equation (II): 3≤x + y≤80 (II), which involves reacting a halogen or halogen-containing gas appearing as a result of the decomposition of a halogen compound with a metal plasma or halogen-containing metal plasma and allowing the resulting compound to deposit as a thin film on a substrate.